The present invention relates to ternary azeotropic, azeotrope-like, or zeotropic compositions of ammonia (NH3), pentafluoroethane (HFC-125) and difluoromethane (HFC-32). The present invention further relates to refrigeration processes using these compositions.
In recent years it has been argued that chlorine-containing refrigerants released into the atmosphere may adversely affect the stratospheric ozone layer. As a result, there is a movement toward the elimination of the use and the production of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) under an international agreement.
Accordingly, there is a demand for the development of refrigerants that have a lower ozone depletion potential than existing refrigerants while still achieving an acceptable performance in refrigeration applications. Hydrofluorocarbons (HFCs) are being used as replacements for CFCs and HCFCs since HFCs contain no chlorine and therefore have zero ozone depletion potential.
In refrigeration applications, refrigerant is often lost during operation through leaks in shaft seals, hose connections, soldered joints and broken lines. In addition, refrigerant may be released to the atmosphere during maintenance procedures on refrigeration equipment. If the refrigerant is not a pure component or an azeotropic or azeotrope-like composition, the composition of the refrigerant may change when leaked or discharged to the atmosphere from the refrigeration equipment, which may cause the refrigerant to become flammable or to have poor refrigeration performance.
Accordingly, it is desirable to use as a refrigerant a single fluorinated hydrocarbon or an azeotropic or azeotrope-like composition that includes two or more fluorinated hydrocarbons. One azeotropic composition already identified as a chlorodifluoromethane (HCFC-22) alternative is a 50/50 weight percent mixture of difluoromethane and pentafluoroethane.
Refrigerant compositions which are non-azeotropic, i.e., zeotropic, may also be useful in certain vapor compression systems. Zeotropic mixtures can boil over a wide temperature range under constant pressure conditions and create a temperature glide in the evaporator and the condenser. This temperature glide can reduce the energy required to operate the system by taking advantage of the Lorenz cycle. The preferred method involves the use of counter flow evaporator and/or condenser heat exchangers in which the refrigerant and heat-transfer fluid flow in a counter-current fashion. This method decreases the temperature difference between the evaporating and condensing refrigerant but maintains a high enough temperature difference between the refrigerant and external heat-transfer fluid to effectively transfer heat. Another benefit of this type of system is that the pressure differences are also minimized. This can result in an improvement in energy efficiency and/or capacity versus conventional systems.
For the foregoing reasons, there is a need for ternary compositions that are useful as refrigerants, and particularly as high-capacity and high-efficiency alternatives to binary compositions of difluoromethane and pentafluoroethane.
The present invention is directed to ternary compositions comprising ammonia, pentafluoroethane, and difluoromethane that satisfy the aforesaid refrigerant needs, as well as high-capacity and high-efficiency alternatives to binary compositions of difluoromethane and pentafluoroethane. The compositions of the present invention include azeotropic, azeotrope-like, and zeotropic compositions of ammonia, pentafluoroethane, and difluoromethane. The present invention further relates to processes for transferring heat using ternary compositions comprising ammonia, pentafluoroethane, and difluoromethane.